The family of IF proteins has five sub-families: four of them are localized in the
cytoplasm and one resides in the nucleus. Cytoplasmic IF proteins such as Vimentin,
Desmin, GFAP, Peripherin, Nestin, Desmuslin,
alpha-Internexin, Neurofilament triplet proteins ( NEFL, NEFM,
NEFH ) form diverse heteropolymers.

Expression patterns of cytoplasmic IFs are cell- and tissue-type specific [1]. Neurofilaments is the principal intermediate filament type expressed by
neurons. They are formed by co-assembly of three subunits: NEFL, NEFM,
and NEFH.

Peripherin is another IF protein expressed mostly in neurons of the peripheral
nervous system. In contrast to neurofilaments, Peripherin can self-assemble to
establish an intermediate filament network. In some cases, Peripherin can assemble
with NEFL. It was suggested that perturbations in the stoichiometry of
neurofilaments can impact Peripherin assembly [2].

Neurofilaments are important protein cargoes for actin -associated motors, such
as myosin, and microtubule -associated motor, such as kinesin in a
complex with Dynactin. These motors are responsible for timely delivery of neural
IF particles and squiggles to all regions of the neuron. Long neural IFs move along
neuritis, albeit more slowly than the precursors.

Munc18, a neuron-specific protein, is independently identified as a
syntaxin-binding protein, that regulates kinase activity of cyclin dependent kinase 5 (
CDK5 ). Munc18 binds to NEFM and NEFH suggesting its role in
the neuron cytoskeletal dynamics.

IF networks are cross-linked by Plectin 1 and BPAG1 that maintain cell
and tissue integrity by coordinated interconnection of three distinct cytoskeletal
filament systems [3].